The prior art is replete with CDMA communication systems, including cellular telephone systems that can handle voice and/or data traffic. Briefly, a CDMA system utilizes binary orthogonal codes to enable multiple users to occupy the same time and frequency allocations within the system. The codes enable a CDMA system to establish multiple communication channels using a shared frequency spectrum. A system configured in accordance with CDMA 1× technology utilizes two primary radio configuration modes to carry information, namely, RC3 and RC4. The RC3 mode utilizes 64 Walsh codes, each of which is 64 bits long. Three of the RC3 Walsh codes are reserved for overhead use, namely, one pilot channel, one paging channel, and one sync channel per base station transceiver subsystem (“BTS”). Consequently, in a practical system, 61 RC3 Walsh codes are available to support user calls.
The RC4 mode utilizes 128 Walsh codes, each of which is 128 bits long. Two related RC4 Walsh codes can be derived from a single RC3 Walsh code. Accordingly, although only 61 RC3 Walsh codes are available to support user calls, 122 RC4 Walsh codes are available to support user calls. The RC4 mode, however, requires more power (on average) per forward link than the RC3 mode. Specifically, RC4 calls require approximately 10% more operating power than RC3 calls. Consequently, older generation CDMA systems having strict power consumption requirements do not support RC4 calls. Furthermore, until recent improvements in practical CDMA system power consumption, a CDMA system that exclusively handled RC3 calls would typically consume all of its available operating power (from the BTS perspective) before exhausting the supply of RC3 Walsh codes. Current systems, however, may assign all of the available RC3 Walsh codes while having excess operating power to spare.
Some existing systems exclusively handle RC4 calls. A practical system that utilizes the RC4 mode for all calls would likely run out of power before exhausting all of the available RC4 Walsh codes. A CDMA system that supports both RC3 and RC4 modes can therefore take advantage of the practical tradeoff between limited system resources for operating power and Walsh code availability. In general, a power limited system that uses a mix of RC3 and RC4 calls can realize a higher capacity than a system that uses only one or the other. In practice, the total number of users, the number of RC3 users, the number of RC4 users, the average power consumption per RC3 user, and the average power consumption per RC4 user will dynamically vary as each BTS in the system establishes new calls, accepts hand-in calls, terminates existing calls, and hands off calls.
Accordingly, it is desirable to have a methodology and system for providing a practical balance of RC3 and RC4 calls within a CDMA system. In addition, it is desirable to have a methodology and system that seeks to minimize or optimize the CDMA system power consumption at all load levels. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.